The present invention relates to a semiconductor having an improved electrode pad, and method of manufacture of device using such.
Conventionally, the electrode pad portion of semiconductor devices connected with package wiring by wire bonding is configured as shown in FIG. 1D.
In FIG. 1D, the numeral 1 represents an oxide film (SiO.sub.2) formed on a silicon (Si) substrate (not shown in the figure), the numeral 2 represents an electrode pad, and the numeral 3 represents a passivation film.
The electrode pad 2 covers the oxide film 1 and is comprised of an aluminum (Al) or Al-Si alloy film for example.
The passivation film 3 is configured from a phosphosilicate glass (PSG) and with the exception of the portion for which wire bonding is performed, is covered by the surface of the electrode pad 2 and the oxide film 1 so that the surface is protected.
Such a structure is formed using the processes shown in FIGS. 1A through 1D.
First, the sputter method is used to deposit Al or Al-Si to a thickness of approximately 8000 .ANG. on the oxide film 1, and the photolithography method is used to form the electrode pads 2 as shown in FIG. 1A. When this is done, the wiring portion (not shown in the figure) is formed to the electrode pad at the same time.
Then, the chemical vapor deposition (CVD) method or a similar method is used to laminate PSG to a thickness of approximately 10000 .ANG. on the oxide film 1 and the electrode pad 2, and form the passivation film 4 as shown in FIG. 1B.
Then, as shown in FIG. 1C, a photoresist 5 is applied to a thickness of approximately 1.5 .mu.m on the passivation film 4 and patterning is implemented, and used as the mask to etch the passivation film 4. By this, the passivation film 4 is made to have an opening only on the electrode pad 2, so that the electrode pad 2 is exposed at this opening portion. After this, the photoresist film 5 is removed to produce the shape shown in FIG. 1D.
Wire bonding is implemented with respect to the exposed portion of the electrode pad 2 of an element of this type. By this, after the wiring processing has been performed, resin encapsulation is performed to form the package, and thus corrosion prevention of the electrode pad 2 is facilitated by this package.
However, when elements are housed inside a package made of a plastic resin, the aluminum (Al) of the pad reacts with halogen ions of chlorine (Cl) and the like, alkali ions such as natrium (Na), and acidic ions such as sulfur oxides (SO.sub.4.sup.-) and the like, to cause faults such as pad corrosion as has been proven in moisture resistance testing for plastic packages.
As has been described above, Cl ions are one of the causes of this corrosion and when this occurs, the reaction is as described below. ##STR1##
Here, the Al(OH).sub.2 Cl is a soluble salt and so assists the progress of corrosion, and brings on element faults and shortens the element life.
Not only this, the size of an electrode pad is normally approximately 100 .mu.m.sup.2 but in order to miniaturize an increase in the chip size and the number of electrode pads, there is the tendency for the pad size to be made smaller but when the pad is of an Al-Si-Cu series alloy, making the pad smaller reduces the positioning surface area for gold (Au) wires in the bonding and causes the problem of facilitating a reduction in the bonding strength.
In addition, when there is an electrode pad of an Al-Si-Cu series alloy, deposition and oxidation of copper (Cu) and the like, obstructs the formation of an Au-Al alloy layer between the surface of the pad and the gold (Au) ball of the bonding portion and so there is also a remarkable decrease in the bonding strength.
It has been thought that these problems could be eliminated by removing the Cu from the alloy material used in the electrode pad. However, the reason why Cu is added to the alloy material used in the electrode pad is so that it can act as a countermeasure to electromigration of the Al wiring, and this Cu is essential for making the wiring finer, and also to reduce the amount of increase in the power consumption.
Therefore, it is necessary to have some countermeasure to prevent the lowering of the bonding strength due to the oxidation and the deposition of the copper, etc. when copper is not removed from the electrode pad alloy material.
In such a conventional semiconductor device as has been described above, the Al of the pad reacts with the halogen ions such as Cl and the like, alkali ions such as Na and the like, and acid ions such as acidic ions such as SO.sub.4.sup.- and the like, to cause the problem of faults such as pad corrosion and the like, and to reduce the Au wire bonding positioning surface area when the pad is made smaller and therefore cause the additional problem of a lowered bonding strength.